Telecommunications systems, cable television systems and data communication networks use optical networks to rapidly convey large amounts of information between remote points. In an optical network, information is conveyed in the form of optical signals through optical fibers. Optical fibers comprise thin strands of glass capable of communicating the signals over long distances with very low loss. Optical networks often employ redundancies to maximize performance and availability. Such redundancies may include optical unidirectional path switched ring (OUPSR). With OUPSR, an optical signal may be transmitted via two or more optical paths between the same source and destination node. An OUPSR device at the destination may include a photodetector per each path to monitor signals received from the two or more paths. Based on such received signals, the OUPSR device may select one of the signals to be forwarded to a transponder or receiver at the destination node. For example, the OUPSR may determine, based on the photodetector monitoring, whether one of the paths has experienced a loss of signal or “loss of light.” If a particular path experiences a loss of light, then the OUPSR may select another path to forward to the transponder or receiver. Such selection may be referred to as a “protection switch.”
In order to accurately detect loss of light, photodetectors must often be of high quality and carefully calibrated. Such calibration adds complexity, time, and cost to the manufacturing process. If high-quality and carefully-calibrated photodetectors are not used, noise introduced into an optical system may cause operational problems in OUPSR. For example, amplified spontaneous emission (ASE) noise may be introduced into an optical network. In certain cases, ASE may further increase in networks including cascaded intermediate line amplifiers (ILAs). In the presence of noise, an OUPSR photodetector may detect light induced by noise even if a failure exists in a particular path, and thus, may not initiate a protection switch. Thus, OUSPR photodetectors must be extremely accurate in order to differentiate between noise and actual signal power.